Apart from altering the attribute 'MAX_HOST_NAME_PREFIX_LENGTH' in providers.json file, it is also required to edit CMU:CloudAdvancedInterface and CMF:CloudServicesFulfillment form in the AR Dev studio.

Please do let me know if it works. If not, open a case with us (cloud support) and will assist you on this

We did this for a customer environment but required someone with really good knowledge of the Remedy Development Studio client and how to modify the right CLM forms. So it's possible, but not something easy to do.